Semiconductor device having an improved connection arrangement between a semiconductor pellet and base substrate electrodes and a method of manufacture thereof

ABSTRACT

A semiconductor device comprising a semiconductor pellet mounted on a pellet mounting area of the main surface of a base substrate, in which first electrode pads arranged on the back of the base substrate are electrically connected to bonding pads arranged on the main surface of the semiconductor pellet. The base substrate is formed of a rigid substrate, and its first electrode pads are electrically connected to the second electrode pads arranged on its reverse side. The semiconductor pellet is mounted on the pellet mounting area of the main surface of the base substrate, with its main surface downward, and its bonding pads are connected electrically with the second electrode pads of the base substrate through bonding wires passing through slits formed in the base substrate.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and a method ofmanufacture thereof and more particularly to a technology effectivelyapplied to a semiconductor device and a method of manufacture thereof,the device having a structure in which a semiconductor pellet is mountedon a pellet mounting area on the main surface of a base substrate and inwhich a first electrode pad on the back of the base substrate iselectrically connected to an external terminal on the main surface ofthe semiconductor pellet.

A semiconductor device with a ball grid array (BGA) structure has beenintroduced as a semiconductor device having a high level of integrationin the Nikkei Electronics, Feb. 28, 1994, pp. 111-117, published byNikkei McGraw-Hill. The BGA structure of such as semiconductor device,as shown in FIG. 16 (cross section of an essential part), has asemiconductor pellet 2 mounted on a pellet mounting area of the mainsurface of the base substrate 1 and a plurality of bump electrodes 4arranged in grid on the back of the base substrate 1 opposite the mainsurface.

The base substrate 1 may be made from a printed wiring board oftwo-layer wiring structure. Second electrode pads 1A are arranged in aperipheral area of the main surface of the base substrate 1 (around thepellet mounting area), while first electrode pads 1B are arranged on theback of the base substrate 1 opposite the main surface. The secondelectrode pads 1A are electrically connected to through-hole conductors1C via conductors 1A₁ arranged on the main surface of the basesubstrate 1. The first electrode pads 1B are electrically connected tothe through-hole conductors 1C via conductors 1B₁ arranged on the backof the base substrate 1.

The semiconductor pellet 2 may comprise mainly a semiconductor substrate2B of single-crystal silicon. On the main surface of the semiconductorsubstrate 2B (device forming surface) is formed a logic circuit system,a memory circuit system or a combination of these. A plurality ofbonding pads 2A are arranged on the main surface of the semiconductorsubstrate 2B. The bonding pads 2A are formed in the top of theinterconnect layers formed on the main surface of the semiconductorsubstrate 2B.

The bonding pads 2A on the semiconductor pellet 2 are electricallyconnected to the second electrode pads 1A on the main surface of thebase substrate 1 through bonding wires 6. In other words, the bondingpads 2A on the semiconductor pellet 2 are electrically connected to thefirst electrode pads 1B through the bonding wires 6, second electrodepads 1A, conductors 1A₁, through-hole conductors 1C and conductors 1B₁.

The semiconductor pellet 2 and the bonding wires 6 are sealed with aresin sealing body 7 formed on the main surface of the base substrate 1.The resin sealing body 7 is formed by transfer molding.

The bump electrodes 4 are electrically and mechanically connected to thesurfaces of the first electrode pads 1B on the base substrate 1. Thebump electrodes 4 may be formed from an alloy material, such as Pb-Sn.

The semiconductor device of such a BGA structure is mounted on amounting board, with the bump electrodes 4 electrically and mechanicallyconnected to electrode pads arranged on the mounting surface of themounting board.

Another example of semiconductor device having a high circuit density isdisclosed in U.S. Pat. Ser. No. 5148265, which shows a semiconductordevice in which the base substrate is made from a filmlike flexiblesubstrate. In this semiconductor device, the semiconductor pellet ismounted, with its main surface downward, on the pellet mounting area ofthe main surface of the base substrate made of a flexible substrate, andthe bonding pads arranged on the main surface of the semiconductorpellet are electrically connected to the second electrode pads arrangedon the back of the base substrate through the bonding wires. The secondelectrode pads on the base substrate are electrically connected to thefirst electrode pads on the back of the base substrate throughconductors that are also arranged on the back. Bump electrodes areelectrically and mechanically connected to the surfaces of the firstelectrode pads.

The semiconductor device of the above construction is mounted on themounting surface of a mounting board, with its bump electrodeselectrically and mechanically connected to the electrode pads arrangedon the mounting surface of the mounting board.

SUMMARY OF THE INVENTION

In the semiconductor device with the BGA structure, as shown in FIG. 16,the second electrode pads 1A arranged on the main surface of the basesubstrate 1 are electrically connected through the through-holeconductors 1C to the first electrode pads 1B arranged on the back of thebase substrate 1. The through-hole conductors 1C comprises a hole areaformed within a through-hole in the base substrate 1 and a land area(fringe portion) formed on the main surface and back surface of the basesubstrate 1. The inner diameter of the through-hole may be around 0.3 mmand the outer diameter of the land area of the through-hole conductor 1Cmay be about 0.6 mm. The inner diameter of the through-hole and theouter diameter of the land area of the through-hole conductor 1C are setlarge compared to the widths of the conductors 1A₁ electricallyconnecting the second electrode pads 1A and the through-hole conductors1C and also compared to the widths of the conductors 1B₁ electricallyconnecting the first electrode pads 1B and the through-hole conductors1C.

The circuit systems formed on the typical semiconductor pellets 2 havetended to grow in their level of integration and the number of functionsthey perform. With enhanced integration and more diversified functionsof the circuit system, the number of bonding pads 2A of thesemiconductor pellet 2 and the number of second electrode pads 1A of thebase substrate 1 increase. That is, the number of through-holeconductors 1C electrically connecting the second electrode pads 1A andthe first electrode pads 1B increases as the integration and function ofthe circuit system are enhanced. Hence, there has been a problem thatthe external size of the base substrate 1 increase with the increasingnumber of the through-hole conductors 1C, which in turn increases thesize of the semiconductor device as a whole.

There is also another problem which the inventors have considered. Theintervals between the through-hole conductors formed by copper foilthick film printing, etching or electroplating techniques are greaterthan the intervals of the bonding pads of the semiconductor pelletformed by photolithography. For this reason, in a semiconductor devicewith the BGA structure, as the number of the through-hole conductors 1Cincreases, they are positioned outwardly away from the semiconductorpellet 2. This inevitably extends the length of the conductors 1A₁electrically connecting the second electrode pads 1A and thethrough-hole conductors 1C and the length of the conductors 1B₁,electrically connecting the first electrode pads 1B and the through-holeconductors 1C. This, in turn, increases inductance and reduces theoperating speed of the semiconductor device.

In the semiconductor device using a flexible substrate for the basesubstrate, the flexible substrate may for example be formed of apolyester film or polyimide film. This flexible substrate has a smallYoung's modulus and is soft (low hardness) compared with a rigidsubstrate impregnated with epoxy resin or polyimide resin, asrepresented by the FR4 substrate according to the NEMA Standard.Therefore, when the bonding pads arranged on the main surface of thesemiconductor pellet are connected with the second electrode padsarranged on the back of the base substrate through bonding wires, thebonding force applied to the second electrode pads is absorbed by thebase substrate, preventing the bonding force and ultrasonic vibrationsfrom being transmitted to the second electrode pads effectively. Thisgives rise to an apprehension that the connection strength between thebonding wires and the second electrode pads may decrease, leading toconnection failures of bonding wires and reduced electric reliability ofthe semiconductor device.

In semiconductor devices that use a flexible substrate for the basesubstrate, the flexible substrate has a large thermal expansioncoefficient in the planar direction and a small Young's modulus (smallrigidity), which means that it is easy to bend, compared with the rigidsubstrate. Therefore, when the semiconductor device is mounted on themounting surface of the mounting board, the reflow heat used during theprocess of mounting causes deformations to the base substrate, such aswarping and twisting, which in turn reduces the flatness of the back ofthe base substrate with respect to the mounting surface of the mountingboard, thereby lowering the mounting precision of the semiconductordevice.

An object of this invention is to provide a technology that allows areduction in the size of the semiconductor device.

Another object of this invention is to provide a technology that allowsan increase in the operating speed of the semiconductor device.

Still another object of this invention is to provide a technology thatcan enhance electric reliability of the semiconductor device.

A further object of this invention is to provide a technology that canenhance mounting precision of the semiconductor device.

A further object of this invention is to provide a manufacturingtechnology for the semiconductor device that can accomplish the aboveobjectives.

These and other objects and novel features of this invention will becomeapparent from the following description of this specification and theaccompanying drawings.

Representative aspects of this invention may be briefly summarized asfollows.

A semiconductor device in accordance with invention comprises asemiconductor pellet mounted on the pellet mounting area of the mainsurface of the base substrate, in which first electrode pads arranged onthe back of the base substrate are electrically connected to the bondingpads on the main surface of the semiconductor pellet. The base substrateis formed of a rigid substrate, and its first electrode pads areelectrically connected to second electrode pads also arranged on theback side of the base subtrate. The semiconductor pellet is mounted,with its main surface downward, on the pellet mounting area of the mainsurface of the base substrate, and its bonding pads are electricallyconnected to the second electrode pads on the base substrate throughbonding wires extending through slits formed in the base substrate.

A method of manufacturing a semiconductor device is also provided, inwhich a semiconductor pellet is mounted on the pellet mounting area ofthe main surface of the base substrate and in which first electrode padsarranged on the back of the base substrate are electrically connected tothe bonding pads on the main surface of the semiconductor pellet. Inparticular, the method includes a step of mounting the semiconductorpellet, with its main surface downward, on the pellet mounting area ofthe main surface of the base substrate made of a rigid substrate, and astep of connecting the bonding pads on the semiconductor pellet to thesecond electrode pads electrically connected to the first electrode padsof the base substrate and arranged on the back of the base substratethrough bonding wires extending through slits formed in the basesubstrate.

According to the above construction of this invention, the bonding padsof the semiconductor pellet and the first electrode pads of the basesubstrate can be electrically connected through the bonding wires andthe second electrode pads, so it is possible to eliminate the throughholes used to electrically connect the second electrode pads and thefirst electrode pads in prior structures. This allows the external sizeof the base substrate to be reduced by an amount corresponding to anarea occupied by the through holes (land area), thus reducing the sizeof the semiconductor device as a whole.

Further, because the first electrode pads can be put closer to thesecond electrode pads by an amount corresponding to an area occupied bythe through holes, the conductors of the base substrate thatelectrically connect the second electrode pads and the first electrodepads can be reduced in length. As a result, inductance can be reducedand the operating speed of the semiconductor device increased.

Further, the rigid substrate has a higher Young's modulus than aflexible substrate; therefore, when the bonding pads arranged on themain surface of the semiconductor pellet and the second electrode padsarranged on the back of the base substrate are electrically connected bybonding wires, the bonding force applied to the second electrode padscan be prevented from being absorbed by the base substrate. This assureseffective transmission of the bonding force and the ultrasonicvibrations to the second electrode pads. Thus, the connection strengthbetween the bonding wires and the second electrode pads is increased,making it possible to prevent connection failure of the bonding wiresand to enhance electric reliability of the semiconductor device.

Furthermore, the rigid substrate has a small inplane thermal expansioncoefficient and a high Young's modulus compared with a flexiblesubstrate, which means the rigid substrate is harder to bend. Thisprevents the base substrate from being deformed (warped or twisted) dueto reflow heat produced during the process of mounting the semiconductordevice on the mounting surface of the mounting board. This ensures asufficient flatness of the back of the base substrate with respect tothe mounting surface of the mounting board, thus enhancing the mountingprecision of the semiconductor device.

According to the above-mentioned manufacturing method of this invention,the bonding pads of the semiconductor pellet and the first electrodepads of the base substrate are electrically connected through bondingwires and second electrode pads, so the through holes electricallyconnecting the second electrode pads and the first electrode pads can beeliminated, making it possible to use a base substrate reduced inexternal size by an amount corresponding to the occupied area of thethrough holes. This in turn allows the manufacture of reduced-sizesemiconductor devices.

Further, because the bonding pads of the semiconductor pellet and thefirst electrode pads of the base substrate are electrically connectedthrough bonding wires and second electrode pads, the through holeselectrically connecting the second electrode pads and the firstelectrode pads can be eliminated, making it possible to use a basesubstrate whose conductors electrically connecting the second electrodepads and the first electrode pads are reduced by a length correspondingto the occupied area of the through holes. This in turn allows themanufacture of semiconductor devices with faster operating speeds.

The base substrate uses a rigid substrate having a high Young's moduluscompared with a flexible substrate; therefore, when the bonding padsarranged on the main surface of the semiconductor pellet and the secondelectrode pads arranged on the back of the base substrate areelectrically connected by bonding wires, the bonding force applied tothe second electrode pads can be prevented from being absorbed by thebase substrate, ensuring effective transfer of the bonding force andultrasonic vibrations to the second electrode pads. This enhances theconnection strength between the bonding wires and the second electrodepads, allowing the manufacture of the semiconductor device with highelectric reliability.

Furthermore, the base substrate used is formed of a rigid substratehaving a small planar thermal expansion coefficient and a high Young'smodulus compared with those of a flexible substrate, which means therigid substrate is harder to bend. As a result, the rigid base substrateis free from deformations (warping or twisting) due to reflow heatduring the process of mounting the semiconductor device on the mountingsurface of the mounting board. As a result, a sufficient degree offlatness of the back of the base substrate with respect to the mountingsurface of the mounting board can be secured, which in turn allows themanufacture of semiconductor devices with high mounting precision.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the main surface side of the semiconductordevice, as a first embodiment of this invention, that employs a BGAstructure;

FIG. 2 is a cross section taken along the line A--A of FIG. 1:

FIG. 3 is an enlarged cross section of an essential part of FIG. 2;

FIG. 4 is an enlarged plan view showing the state of the back side of anessential part of the semiconductor device with the resin sealing bodyremoved;

FIG. 5 is a cross section showing an essential part of a molding die forthe resin sealing body of the semiconductor device;

FIG. 6 is a cross section showing the method of manufacturing thesemiconductor device;

FIG. 7 is a cross section of an essential part of the semiconductordevice showing the method of manufacture thereof;

FIG. 8 is a cross section of an essential part of the semiconductordevice showing the method of manufacture thereof;

FIG. 9 is a cross section of an essential part of the semiconductordevice showing the method of manufacture thereof; FIG. 10 is a crosssection showing an essential part of the semiconductor device mounted ona mounting board;

FIG. 11 is a cross section showing a variation of the semiconductordevice;

FIG. 12 is a cross section of the semiconductor device, as a secondembodiment of this invention, that employs the BGA structure;

FIG. 13 is an enlarged plan view showing the state of the back side ofan essential part of the semiconductor device with the resin sealingbody removed;

FIG. 14 is a plan view showing the state of the back side of anessential part of the semiconductor device, as a third embodiment ofthis invention, that employs the BGA structure with the resin sealingbody removed;

FIG. 15 is a plan view showing the state of the back side of anessential part of the semiconductor device, as a fourth embodiment ofthis invention, that employs the BGA structure and is removed of theresin sealing body removed; and

FIG. 16 is a cross section showing an essential part of thesemiconductor device that employs the conventional BGA structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The construction of this invention is described in the following inconjunction with embodiments that apply this invention to asemiconductor device using the BGA structure.

In the drawings used for explaining the embodiments, components withidentical functions are given like reference numerals and theirexplanations are not repeated.

Embodiment 1

The outline construction of a semiconductor device, as a firstembodiment of this invention, that uses the BGA structure is shown inFIG. 1 (plan view of the main surface side), FIG. 2 (cross section takenalong the line A--A of FIG. 1), FIG. 3 (enlarged cross section of anessential part of FIG. 2) and FIG. 4 (enlarged plan view showing theback side of an essential part of the semiconductor device with theresin sealing body removed).

As shown in FIGS. 1, 2, 3 and 4, the semiconductor device has asemiconductor pellet 2 mounted on a pellet mounting area of the mainsurface of a base substrate 1, with a plurality of bump electrodes 4arranged in grid on the back of the base substrate 1 opposite the mainsurface.

The base substrate 1 may be formed of a printed circuit board. Theprinted circuit board may, for example, have a structure in which wiringis formed over the surface of a rigid substrate of glass fiberimpregnated with epoxy resin, polyimide resin or maleimide resin. Inother words, the base substrate 1 is formed of a rigid substrate. Therigid substrate has a high Young's modulus and is hard compared with aflexible substrate made of polyester film or polyimide film. The rigidsubstrate has a small thermal expansion coefficient in a planardirection, a high Young's modulus and is difficult to bend compared withthe flexible substrate. For example, the rigid substrate made of a glassfiber impregnated with epoxy resin or polyimide resin has a Young'smodulus of around 16-22 GPa and a thermal expansion coefficient of about10-20×10⁻⁶ 1/° C. Flexible substrates made of polyester film orpolyimide film have a Young's modulus of about 2-5 GPa and a thermalexpansion coefficient of about 20-25×10⁻⁶ 1/° C.

On the back of the base substrate 1 are formed a plurality of secondelectrode pads 1A and first electrode pads 1B, which are electricallyinterconnected through conductors 1B₁ on the back of the basesubstrate 1. The second electrode pads 1A, first electrode pads 1B andconductors 1B₁ are formed of a Cu film, for example.

On the surfaces of the first electrode pads 1B are formed bumpelectrodes 4 that are electrically and mechanically connected to them.The bump electrodes 4 may be formed of, for instance, a Pb-Sn alloy.

The semiconductor pellet 2 is mounted, with its main surface (undersidein FIG. 2 and 3) downward, on the pellet mounting area of the mainsurface of the base substrate 1. That is, the semiconductor pellet 2 ismounted facedown on the pellet mounting area of the main surface of thebase substrate 1. Interposed between the main surface of thesemiconductor pellet 2 and the pellet mounting area of the main surfaceof the base substrate 1 is an insulating layer 3, which may be formed ofa polyimide-, epoxy- or silicon-base low-elasticity resin.

The semiconductor pellet 2 may be rectangular and may mainly becomprised of a semiconductor substrate 2B made of single-crystalsilicon. On the main surface (device forming surface) of thesemiconductor substrate 2B are formed a logic circuit system, a memorycircuit system or a combination of these. Also on the main surface ofthe semiconductor substrate 2B, a plurality of bonding pads 2A arearranged along the sides of the rectangular surface. The bonding pads 2Aare formed on the top of interconnect layers on the main surface of thesemiconductor substrate 2B. That is, the bonding pads 2A are arranged inthe periphery of the main surface of the semiconductor pellet 2 alongeach of the four sides.

The bonding pads 2A of the semiconductor pellet 2 and the secondelectrode pads 1A of the base substrate 1 are electrically connected toeach other through bonding wires 6 running in slits 5 formed in the basesubstrate 1. The bonding wires 6 may be of gold (AU), copper (Cu) oraluminum (Al), and may be coated with insulating resin. The bondingwires 6 may be connected by a bonding method that utilizes ultrasonicvibrations in combination with thermocompression.

The slits 5 in the base substrate 1 are formed in the directions of therows of the bonding pads 2A that are arranged along each side of themain surface of the semiconductor pellet 2. That is, the base substrate1 of this embodiment has four slits 5, each of which is located abovethe bonding pads 2A of the semiconductor pellet 2.

The second electrode pads 1A of the base substrate 1 are placed in bothareas of the back of the base substrate 1 divided by the slits 5. Thesecond electrode pads 1A located in one of the areas of the back of thebase substrate 1 demarcated by the slits 5 (inside the semiconductorpellet 2) are supplied with a power supply such as an operation voltage(3.3 V for instance) and a reference voltage (0 V for instance). Thesecond electrode pads 1A located in the other area of the back of thebase substrate 1 demarcated by the slits 5 (outside the semiconductorpellet 2) receive a signal such as an input/output signal and a controlsignal.

The semiconductor pellet 2 are provided with 100 bonding pads 2A on eachside at a pitch of about 100 μm. The number of bonding pads 2A isincreased as the level of integration and the operating speed of thecircuit system mounted on the semiconductor pellet 2 increase.

The first area of the back of the base substrate 1 demarcated by theslits 5 is provided with, for example, 50 second electrode pads 1A foreach side of the semiconductor pellet 2; and the second area is providedwith, for instance, 50 second electrode pads 1A for each side of thesemiconductor pellet 2. Because the second electrode pads 1A cannot bemade as small as the bonding pads 2A of the semiconductor pellet 2, thepitch of the second electrode pads 1A is set wider than that of thebonding pads 2A, for instance, at around 200 μm. That is, because thesecond electrode pads 1A of the base substrate 1 are arranged in tworows for each side of the semiconductor pellet 2, the length of thesecond electrode pads 1A corresponding to one side of the semiconductorpellet 2 can be made almost equal to that of the bonding pads 2Aarranged along one side of the semiconductor pellet 2 even if the pitchof the second electrode pads 1A of the base substrate 1 is set to twotimes that of the bonding pads 2A of the semiconductor pellet 2.Furthermore, the second electrode pads 1A of the base substrate 1 can belocated at positions facing the corresponding bonding pads 2A of thesemiconductor pellet 2.

The peripheral area of the main surface of the base substrate 1excluding the pellet mounting area is covered with a resin sealing body7, which seals the bonding wires 6. That is, the resin sealing body 7 isformed on the main surface side and the back surface side of the basesubstrate 1. The resin sealing body 7 is made from epoxy resin 7Acontaining a phenol-base hardener, silicone rubber and filler forreducing stresses.

The back of the base substrate 1 facing the main surface of thesemiconductor pellet 2 is exposed from the resin sealing body 7 thatcovers the peripheral area of the base substrate 1.

The resin sealing body 7 is formed by the transfer molding that uses amolding die 10 shown in FIG. 5 (cross section of an essential part). Themolding die 10 has a cavity 11 defined by an upper die 10A and a lowerdie 10B, an inflow gate 13 connected to the cavity 11, and, though notshown, a pot and a runner. The pot communicates with the cavity 11through the runner and the inflow gate 13.

The cavity 11 comprises a recess 11A formed in the upper die 10A and arecess 11B formed in the lower die 10B. The resin 7A is supplied intothe recess 11A from the pot through the runner and the inflow gate 13.The base substrate 1 is placed in the recess 11B.

The recess 11B is formed with recesses 12, which are located atpositions facing the slits 5 of the base substrate 1 and which extend inthe same directions as the slits 5. Placed in the recesses 12 are a partof bonding wires 6 electrically connecting the bonding pads 2A of thesemiconductor pellet 2 and the second electrode pads 1A of the basesubstrate 1, and also the second electrode pads 1A of the basesubstrate 1. The resin 7A is supplied from the recess 11A through theslits 5 of the base substrate 1 into the recess 11A.

Though not shown in FIG. 12, the recesses 12 are provided with a gasvent to prevent voids due to bubbles.

Next, the method of manufacturing the above-mentioned semiconductordevice is described by referring to FIGS. 6 through FIG. 9.

First, a base substrate 1 made of a rigid substrate is prepared. Thebase substrate 1 includes slits 5 as well as second electrode pads 1A,first electrode pads 1B and conductors 1B₁ on its back.

Next, as shown in FIG. 6 (cross section), the semiconductor pellet 2 ismounted on the pellet mounting area of the main surface of the basesubstrate 1. The semiconductor pellet 2 is fixed to the pellet mountingarea of the main surface of the base substrate 1 through an insulatinglayer 3.

Next, the base substrate 1 is mounted on a bonding stage (heat block) 14with the semiconductor pellet 2 at the bottom. The bonding stage 14 hasa recess 14A that accommodates the semiconductor pellet 2. The basesubstrate 1 and the semiconductor pellet 2 are heated to about 200° C.on the bonding stage 14.

Next, as shown in FIG. 7 (cross section of an essential part), thebonding pads 2A arranged on the main surface of the semiconductor pellet2 and the second electrode pads 1A arranged on the back of the basesubstrate 1 are electrically connected by the bonding wires 6. Thebonding wires 6 running in the slits 5 are connected to the bonding pads2A of the semiconductor pellet 2 and to the second electrode pads 1A ofthe base substrate 1. The connection of the bonding wires 6 isaccomplished by ultrasonic thermocompression bonding. In this process,the base substrate 1 is made from a rigid substrate with a high Young'smodulus compared with the flexible substrate used in conventionalstructure, so that the bonding force applied to the second electrodepads 1A is prevented from being absorbed by the rigid base substrate 1,thus allowing the bonding force and the ultrasonic vibrations to betransferred effectively to the second electrode pads 1A. Further,because the base substrate 1 is made of a rigid substrate that has asmaller thermal expansion coefficient in the planar direction than thatof a flexible substrate and a higher Young's modulus--which means it isharder to bend--it is possible to reduce positional deviations of thesecond electrode pads 1A and of the bonding pads 2A of the semiconductorpellet 2 due to thermal expansion of the base substrate 1.

Then, as shown in FIG. 8 (cross section of an essential part), the basesubstrate 1 and the semiconductor pellet 2 are put in the cavity 11defined by the upper die 10A and the lower die 10B of the molding die10, with the base substrate 1 fit in the recess 11B of the cavity 11. Apart of the bonding wires 6 and the second electrode pads 1A of the basesubstrate 1 are placed in the recesses 12 formed in the recess 11B. Themolding die 10 is preheated to around 170°-180° C. to heighten thefluidity of the resin 7A supplied into the cavity 11. Because the basesubstrate 1 is made from a rigid substrate with a smaller thermalexpansion coefficient in the planar direction than the flexiblesubstrate and with a higher Young's modulus, which means the basesubstrate 1 is harder to bend, the base substrate 1 can be preventedfrom being deformed (warped or twisted) due to the heating of themolding die 10 to about 170°-180° C. during this process.

Next, resin tablets are charged into the pot of the molding die 10,nothing that they are preheated by a heater to lower the viscositybefore being charged. The resin tablets in the pot are heated by themolding die 10, further lowering the viscosity.

The resin is then pressurized by a plunger of the transfer moldingdevice, forcing the resin 7A from the pot through the runner and thegate 13 into the recess 11A and the recesses 12 of the cavity 11 tocover the peripheral area of the main surface of the base substrate 1,leaving the back of the semiconductor pellet 2 exposed. In this way, aresin sealing body 7 that seals the bonding wires 6 is formed. The resin7A is forced into the recesses 12 through the slits 5 of the basesubstrate 1 from the recess 11A. In this process, the resin 7A suppliedfrom the recess 11A to the recesses 12 through the slits 5 flows in theaxial direction of the bonding wires 6, i.e., in the vertical direction,from one end side of the bonding wires 6. This vertical flow of resinprevents the bonding wires 6 from being deformed whereas the horizontalflow along the surface of the base substrate 1 may deform them.

Then, the base substrate 1 is taken out of the molding die 10, and bumpelectrodes 4 are electrically and mechanically connected to the surfacesof the first electrode pads 1B on the back of the base substrate 1.Thus, a nearly completed semiconductor device shown in FIG. 1, 2, 3 and4 is obtained.

After this, the semiconductor device is shipped as a product. Thesemiconductor device shipped as a product is mounted on a mountingsurface of a mounting board 15, with the bump electrodes 4 of thesemiconductor device electrically and mechanically connected toelectrode pads 15A arranged on the mounting surface of the mountingboard 15, as shown in FIG. 10 (cross section). The connection betweenthe bump electrodes 4 of the semiconductor device and the electrode pads15A of the mounting board 15, although it depends on the material of thebump electrodes 4, may be accomplished in an atmosphere at a reflowtemperature of, for instance, around 210°-230° C. In this mountingprocess, because the base substrate 1 is made from a rigid substratewhich has a smaller thermal expansion coefficient in the planardirection and a higher Young's modulus--which means it is more difficultto bend--than a flexible substrate, the base substrate 1 can beprevented from being deformed due to reflow heat.

This embodiment offers the following advantages.

A semiconductor device comprises a semiconductor pellet 2 mounted on apellet mounting area of the main surface of a base substrate 1, in whichfirst electrode pads 1B arranged on the back of the base substrate 1 areelectrically connected to bonding pads 2A arranged on the main surfaceof the semiconductor pellet 2. The base substrate 1 is formed of a rigidsubstrate, and its first electrode pads 1B are electrically connected tothe second electrode pads 1A arranged on its reverse side. Thesemiconductor pellet 2 is mounted on the pellet mounting area of themain surface of the base substrate 1, with its main surface downward,and its bonding pads 2A are electrically connected with the secondelectrode pads 1A of the base substrate 1 through bonding wires 6passing through slits 5 formed in the base substrate 1. Because withthis construction the bonding pads 2A of the semiconductor pellet 2 andthe first electrode pads 1B of the base substrate 1 can be electricallyconnected through the bonding wires 6 and second electrode pads 1A, itis possible to eliminate the through holes used to electrically connectthe second electrode pads 1A and the first electrode pads 1B. This inturn allows the base substrate 1 to be reduced in size by an amountcorresponding to the occupied area of the through holes (land area),which contributes to size reduction of the semiconductor device.

Because the first electrode pads 1B can be put closer to the secondelectrode pads 1A by a distance corresponding to the occupied area ofthe through holes, it is possible to shorten the length of theconductors 1B, of the base substrate 1 that electrically connect thesecond electrode pads 1A and the first electrode pads 1B. This reducesthe inductance, increasing the operation speed of the semiconductordevice.

Further, because the rigid substrate has a higher Young's modulus and isharder than the flexible substrate of the conventional structure, thebonding force applied to the second electrode pads 1A is not absorbed bythe base substrate 1 when electrically connecting the bonding pads 2A onthe main surface of the semiconductor pellet 2 and the second electrodepads 1A on the back of the base substrate 1 by the bonding wires 6. As aresult, the bonding force and the ultrasonic vibrations are effectivelytransferred to the second electrode pads 1A. This in turn increases theconnection strength between the bonding wires 6 and the second electrodepads 1A, preventing possible connection failures of the bonding wires 6,enhancing the electric reliability of the semiconductor device.

Moreover, because the rigid substrate has a smaller thermal expansioncoefficient in the planar direction and a higher Young's modulus than aflexible substrate, which means it is more resistant to bending, thebase substrate 1 is free from deformations (warping and twisting) due toreflow heat when the semiconductor device is mounted on the mountingsurface of the mounting board 15. As a result, a sufficient degree offlatness of the back of the base substrate 1 with respect to themounting surface of the mounting board 15 can be secured, enhancing themounting precision of the semiconductor device.

Further, because the rigid substrate has a smaller thermal expansioncoefficient in the planar direction and a higher Young's modulus thanthe flexible substrate, which means it is more resistant to bending, thewarping of the base substrate 1 can be limited to less than 100 μm evenwhen the external size of the base substrate 1 increases with theincreasing number of the first electrode pads 1B.

With the warping of the base substrate 1 limited to within 100 μm, it ispossible to eliminate a reinforcement substrate intended to preventwarping of the base substrate 1. This reduces the manufacture cost ofthe semiconductor device compared with that of a semiconductor devicehaving a reinforcement substrate.

Furthermore, because the base substrate 1 can be formed of a printedwiring board of a single layer structure having the second electrodepads 1A, first electrode pads 1B and conductors 1B₁ arranged only on theback of a rigid substrate, the parts cost of the base substrate 1 can bereduced compared with that of a base substrate formed of a two-layerprinted wiring board which has circuits formed on both the main and backsurfaces of the rigid substrate. This means that the overall cost ofsemiconductor device manufacture can be lowered.

Another feature of this embodiment is that the slits 5 formed in thebase substrate 1 extend in the directions of rows of bonding pads 2Aarranged on the main surface of the semiconductor pellet 2 and arelocated at positions over the bonding pads 2A. With this construction,the slits 5 are arranged within the area occupied by the semiconductorpellet 2, so that the base substrate 1 requires no increase in sizecorresponding to the slits 5.

A further feature of this embodiment is that the second electrode pads1A are arranged in two opposite areas of the back of the base substrate1 divided by the slits 5. This construction allows an increase in thenumber of power supply paths for electrically connecting the bondingpads 2A of the semiconductor pellet 2 and the second electrode pads 1Aof the base substrate 1. This in turn makes it possible to reduce powersupply noise generated at time of simultaneous switching of signals,thereby preventing malfunctions of the semiconductor device.

Further, even when the pitch of the second electrode pads 1A of the basesubstrate 1 is set larger than that of the bonding pads 2A of thesemiconductor pellet 2, the length of the row of the second electrodepads 1A for each side of the semiconductor pellet 2 can be made almostequal to the length of the row of the bonding pads 2A for each side ofthe semiconductor pellet 2. This prevents an increase in the length ofthe bonding wires 6, which is dependent on the length of the row of thesecond electrode pads 1A. As a result, it is possible to prevent thebonding wires 6 from being deformed by the flow of resin when thebonding wire 6 are sealed by the resin sealing body 7 according to thetransfer molding.

Further, because the second electrode pads 1A can be located atpositions on the base substrate 1 facing the bonding pads 2A of thesemiconductor pellet 2, the lengths of the bonding wires 6 can be madeuniform, which in turn makes uniform the inductances of the signal pathsbetween the bonding pads 2A of the semiconductor pellet 2 and the secondelectrode pads 1A of the base substrate 1.

A further feature of this embodiment is the structure in which the backof the semiconductor pellet 2 opposing its main surface is exposed fromthe resin sealing body 7 that covers the peripheral area around the mainsurface of the base substrate 1. This structure allows the heatgenerated by the operation of the circuit system mounted on thesemiconductor pellet 2 to be released from the back of the semiconductorpellet 2, thus enhancing the heat dissipation efficiency of thesemiconductor device.

Further, because the mechanical strength of the base substrate 1 can bereinforced by the mechanical strength of the resin sealing body 7,deformations of the base substrate 1 (warping and twisting) due toreflow heat during mounting can be prevented.

A further feature of this embodiment is that the bonding wires 6 aresealed with the resin sealing body 7. This structure prevents thebonding wires 6 from being deformed due to external impacts andcontacts, thus enhancing the electric reliability of the semiconductordevice.

A still further feature of this embodiment is that the resin sealingbody 7 is formed both on the main surface side and the back surface sideof the base substrate 1. This structure prevents the resin sealing body7 from becoming separated from the base substrate 1 due to the thermalstresses generated during a temperature cycle test or when the bumpelectrodes 4 are connected. This in turn enhances the reliability of thesemiconductor device.

A method of manufacturing a semiconductor device, in which asemiconductor pellet 2 is mounted on a pellet mounting area of the mainsurface of a base substrate 1 and in which first electrode pads 1Barranged on the back of the base substrate 1 are electrically connectedto bonding pads 2A arranged on the main surface of the semiconductorpellet 2, comprises a step of mounting the semiconductor pellet 2, withits main surface downward, on the pellet mounting area of the mainsurface of the base substrate 1 formed of a rigid substrate, and a stepof electrically connecting the bonding pads 2A to the second electrodepads 1A, which are electrically connected to the first electrode pads 1Bof the base substrate 1 and arranged on the back of the base substrate1, through bonding wires 6 passing through slits 5 formed in the basesubstrate 1. The bonding pads 2A of the semiconductor pellet 2 and thefirst electrode pads 1B of the base substrate 1 therefore areelectrically connected through the bonding wires 6 and the secondelectrode pads 1A, so that through holes 1C used for electricallyconnecting the second electrode pads 1A and the first electrode pads 1Bcan be eliminated, reducing the external size of the base substrate 1 byan amount corresponding to the occupied area of the through holes. As aresult, the overall external size of the semiconductor device can bereduced.

Further, because the bonding pads 2A of the semiconductor pellet 2 andthe first electrode pads 1B of the base substrate 1 are electricallyconnected through the bonding wires 6 and the second electrode pads 1A,there is no need for through holes 1C to electrically connect the secondelectrode pads 1A with the first electrode pads 1B. This makes itpossible to use a base substrate 1 in which the conductors 1B₁electrically connecting the second electrode pads 1A and the firstelectrode pads 1B are shorter by a length corresponding to the occupiedarea of the through holes. As a result, it is possible to fabricate asemiconductor device with fast operating speeds.

Because the base substrate 1 used is formed of a rigid substrate havinga higher Young's modulus--which means it is harder--than a flexiblesubstrate, the bonding force applied to the bonding pads 2A whenelectrically connecting the bonding pads 2A arranged on the main surfaceof the semiconductor pellet 2 and the second electrode pads 1A arrangedon the back of the base substrate 1 through the bonding wires 6 is notabsorbed by the base substrate 1, effectively transmitting the bondingforce and ultrasonic vibrations to the second electrode pads 1A. As aresult, the connection strength between the bonding wires 6 and thesecond electrode pads 1A can be increased, which in turn allows themanufacture of a semiconductor device with high electric reliability.

Because the base substrate 1 is formed of a rigid substrate having asmaller thermal expansion coefficient in the planar direction and ahigher Young's modulus--which means it is more resistant tobending--than a flexible substrate, the base substrate 1 is preventedfrom being deformed (warped or twisted) due to reflow heat during theprocess of mounting the semiconductor device on the mounting surface ofthe mounting board 15. This allows the back surface of the basesubstrate 1 to have a sufficient degree of flatness with respect to themounting surface of the mounting board 15, thus enhancing the mountingprecision of the semiconductor device.

Following the process of electrically connecting with the bonding wires6, the method of manufacture includes a process of transfer molding of aresin sealing body 7 that covers the peripheral area of the main surfaceof the base substrate 1 and seals the bonding wires 6. Because the basesubstrate 1 uses a rigid substrate which has a smaller thermal expansioncoefficient in the planar direction and a higher Young's modulus and ismore resistant to bending than a flexible substrate, this methodprevents the base substrate 1 from being deformed (warped or twisted)due to heating of the molding die 10.

Because the resin 7A supplied from the recess 11A into the recesses 12through the slits 5 flows from one end side of the bonding wires 6 intheir axial direction, i.e., in the vertical direction, the bondingwires 6 are not deformed by the flow of the resin 7A, whereas they canbe deformed when the resin flows along the surface of the base substrate1, i.e., in the lateral direction.

As shown in FIG. 11 (cross section), the resin sealing body 7 may beformed on the back surface of the base substrate 1 excluding thesurfaces of the second electrode pads 1A and first electrode pads 1B. Inthis case, the base substrate 1 is held and clamped from both sides bythe resin sealing body 7 and therefore prevented from being warped.

The base substrate 1 may, though not shown, be formed in a multilayerstructure in which a plurality of rigid substrates are stacked together.This structure can reduce the manufacture cost as compared with a basesubstrate made up of a plurality of flexible substrates stackedtogether.

Embodiment 2

The outline configuration of a semiconductor device as the secondembodiment of this invention that employs a BGA structure is shown inFIG. 12 (cross section) and FIG. 13 (enlarged plan view of an essentialpart of the back side showing the state of the back side removed of theresin sealing body).

As shown in FIG. 12 and 13, the semiconductor device has thesemiconductor pellet 2 mounted facedown on the pellet mounting area ofthe main surface of the base substrate 1 with an insulating layer 3 inbetween. A plurality of bump electrodes 4 are arranged in grid on theback of the base substrate 1.

Arranged in the central area of the main surface of the semiconductorpellet 2 along the longer sides thereof is a row of bonding pads 2A,which are electrically connected to the second electrode pads 1Aarranged on the back of the base substrate 1 through the bonding wires 6passing through the slits 5 formed in the base substrate 1. The secondelectrode pads 1A are electrically connected to the corresponding firstelectrode pads 1B arranged on the back of the base substrate 1 throughconductors 1B₁. Bump electrodes 4 are electrically and mechanicallyconnected to the surfaces of the first electrode pads 1B. That is, thebonding pads 2A of the semiconductor pellet 2 are electrically connectedto the first electrode pads 1B through the bonding wires 6, secondelectrode pads 1A and conductors 1B₁.

The slits 5 of the base substrate 1 are formed in the central area ofthe main surface of the semiconductor pellet 2 along the direction ofthe row of the bonding pads 2A arranged along the longer side of thesemiconductor pellet 2. The slits 5 are tapered so that its opening onthe back side of the base substrate 1 is greater than the opening on themain surface side.

As described above, this embodiment offers similar effects andadvantages to those of the first embodiment. With the slits 5 tapered,it is possible to prevent contact between the base substrate 1 and abonding tool when one end of the bonding wires 6 is bonded to thebonding pads 2A of the semiconductor pellet 2. This in turn raises theyield of semiconductor device assembly in the bonding process.

Embodiment 3

The outline configuration of a semiconductor device as the thirdembodiment of this invention that employs a BGA structure is shown inFIG. 14 (plan view of an essential part of the back side showing thestate of the back side removed of the resin sealing body).

As shown in FIG. 14, the semiconductor device has a semiconductor pellet2 mounted facedown on a pellet mounting area of the main surface of thebase substrate 1, with an insulating layer 3 in between. Bump electrodes4 are arranged in grid on the back of the base substrate 1.

At the outer periphery of the main surface of the semiconductor pellet2, a plurality of bonding pads 2A are arranged along the sides of thepellet. At the central portion of the main surface of the semiconductorpellet 2, a plurality of bonding pads 2A are arranged along the longeror shorter side of the pellet. The bonding pads 2A are electricallyconnected to the second electrode pads 1A arranged on the back of thebase substrate 1 by bonding wires 6 passing through slits 5 formed inthe base substrate 1. The second electrode pads 1A are electricallyconnected to first electrode pads 1B arranged on the back of the basesubstrate 1 through conductors 1B₁. Bump electrodes 4 are electricallyand mechanically connected to the surfaces of the individual firstelectrode pads 1B. That is, the bonding pads 2A are electricallyconnected to the first electrode pads 1B through the bonding wires 6,second electrode pads 1A and conductors 1B₁.

The slits 5 are arranged at each sides of the semiconductor pellet 2 andalso at the central portion of the pellet. That is, the base substrate 1of this embodiment has five slits 5, each of which is located above thebonding pads 2A of the semiconductor pellet 2.

As explained above, this embodiment offers the similar effects andadvantages to those of the first embodiment. Because the slits 5 arearranged at the sides and the central portion of the semiconductorpellet 2, it is possible to increase the number of bonding pads 2Aarranged on the main surface of the semiconductor pellet 2 and thenumber of second electrode pads 1A arranged on the back of the basesubstrate 1. This allows an increase in the number of power supply pathsfor electrically connecting the bonding pads 2A of the semiconductorpellet 2 and the second electrode pads 1A of the base substrate 1. Thisis turn allows a further reduction in power supply noise generated whenoutput signals are switched simultaneously. Furthermore, thisconstruction makes it possible to increase the number of signal pathselectrically connecting the bonding pads 2A of the semiconductor pellet2 and the second electrode pads 1A of the base substrate 1 and thereforereduce the external size of the semiconductor pellet 2 dictated by thenumber of bonding pads 2A.

Although this embodiment has been shown to have only one slit 5 formedat the central portion of the semiconductor pellet 2, two or more slits5 may be arranged parallelly or crosswise to each other at the centralpart of the semiconductor pellet 2. By increasing the number of slits 5in this way, it is possible to further increase the number of the secondelectrode pads 1A of the base substrate 1 and the number of the bondingpads 2A of the semiconductor pellet 2.

Embodiment 4

The outline configuration of a semiconductor device as the fourthembodiment of this invention that employs a BGA structure is shown inFIG. 15 (plan view of an essential part of the back side showing thestate of the back side removed of the resin sealing body).

As shown in FIG. 15, the semiconductor device has a semiconductor pellet2 mounted facedown on a pellet mounting area of the main surface of thebase substrate 1, with an insulating layer 3 in between. Bump electrodes4 are arranged in grid on the back of the base substrate 1. The basesubstrate 1 is formed of a printed circuit board of, for example,3-layer wiring structure.

At the outer periphery of the main surface of the semiconductor pellet2, a plurality of bonding pads 2A are arranged along the sides of thepellet. The bonding pads 2A are electrically connected to the secondelectrode pads 1A arranged on the back of the base substrate 1 throughbonding wires 6 passing through slits 5 formed in the base substrate 1.

Of the second electrode pads 1A, electrode pads 1A₂ are formed integralwith electrode plates 8A. The electrode plates 8A are electricallyconnected to other electrode plates 8A via through holes (not shown) andinternal wiring (not shown) in the base substrate 1. The electrodeplates 8A is connected to be at a reference voltage (0 V for example).Of the second electrode pads 1A, electrode pads 1A₃ are formed integralwith an electrode plate 8B. This electrode plate 8A is connected to beat an operating voltage (3.3 V for instance).

With this embodiment, because the through holes 1C that electricallyconnect the second electrode pads 1A on the main surface of the basesubstrate 1 and the first electrode pads 1B on the back are eliminated,the electrode plates 8A and the electrode plate 8B can be arranged onthe back of the base substrate 1. This allows the bump electrodes 4 tobe freely located and shortens the distance between the bonding pads 2Aof the semiconductor pellet 2 and the pump electrodes 4. As a result,the inductance can be reduced, thereby increasing the operating speedsof the semiconductor device.

The invention has been described in detail in connection withrepresentative embodiments of the invention. It is noted, however, thatthe invention is not limited to these embodiments but that manymodifications may be made without departing from the spirit of theinvention.

Representative advantages of this invention may be summarized asfollows.

It is possible to reduce the size of a semiconductor device in which thesemiconductor pellet is mounted on the pellet mounting area of the mainsurface of the base substrate and in which the first electrode padsarranged on the back of the base substrate are electrically connected tothe bonding pads arranged on the main surface of the semiconductorpellet.

It is possible to increase the operating speed of the semiconductordevice.

It is also possible to enhance the electric reliability of thesemiconductor device.

Further, it is possible to increase the mounting precision of thesemiconductor device.

What is claimed is:
 1. A semiconductor device comprising:(a) a rigidsubstrate having a first main surface and a second main surface oppositeto the first main surface; (b) a semiconductor pellet mounted on thefirst main surface of the rigid substrate, the semiconductor pellethaving a plurality of semiconductor circuit elements and a plurality ofbonding pads; (c) a plurality of electrode pads formed on the secondmain surface of the rigid substrate; and (d) a plurality of bondingwires for electrically connecting the bonding pads of the semiconductorpellet with the electrode pads; wherein the semiconductor pellet ismounted facedown on the rigid substrate, the rigid substrate has slitsthat extend from the first main surface to the second main surface andexpose the bonding pads of the semiconductor pellet, the bonding wiresextend through the slits in the rigid substrate to connect the bondingpads and the electrode pads, and bump electrodes are formed on saidelectrode pads.
 2. A semiconductor device according to claim 1, whereinthe bonding pads are arranged at the periphery of the semiconductorpellet and the slits are formed along the directions of rows of thebonding pads.
 3. A semiconductor device according to claim 2, whereinthe electrode pads are located on both sides of the slits.
 4. Asemiconductor device according to claim 3, wherein the electrode padslocated on one side of the slits and under the semiconductor pellet arepower supply pads, and the electrode pads located on the other side ofthe slits and outside the semiconductor pellet are signal pads.
 5. Asemiconductor device according to claim 1, further comprising a firstresin sealing body covering the semiconductor pellet.
 6. A semiconductordevice according to claim 5, further comprising a second resin sealingbody formed in the slits and covering the bonding wires.
 7. Asemiconductor device according to claim 1, wherein said rigid substrateis formed by glass fibers impregnated with epoxy resin.
 8. A method ofmanufacturing a semiconductor device in which a semiconductor pellet ismounted on a pellet mounting area of the main surface of a rigid basesubstrate and in which first electrode pads arranged on the back of therigid base substrate are electrically connected to bonding pads arrangedon the main surface of the semiconductor pellet, said methodcomprising:a step of mounting the semiconductor pellet, with its mainsurface downward, on the pellet mounting area of the main surface of therigid base substrate a step of electrically connecting the bonding padsof the semiconductor pellet and second electrode pads electricallyconnected to the first electrode pads of the rigid base substrate andarranged on the back of the rigid base substrate through bonding wirespassing through slits formed on the rigid base substrate; and a step offorming bump electrodes on the first electrode pads.
 9. A method ofmanufacturing a semiconductor device according to claim 9, furthercomprising a step of forming by transfer molding a resin sealing bodythat covers the periphery of the main surface of the rigid basesubstrate and seals the bonding wires, after the step of electricallyconnecting the bonding wires.
 10. A semiconductor device according toclaim 10, wherein said rigid substrate is formed by glass fibersimpregnated with polyimide resin.
 11. A semiconductor devicecomprising:(a) a rigid substrate having a first main surface and asecond main surface opposite to the first main surface; (b) asemiconductor pellet mounted on the first main surface of the rigidsubstrate, the semiconductor pellet having a plurality of semiconductorcircuit elements and a plurality of bonding pads; (c) a plurality ofelectrode pads formed on the second main surface of the rigid substrate;and (d) a plurality of bonding wires for electrically connecting thebonding pads of the semiconductor pellet with the electrode pads;wherein the semiconductor pellet is mounted facedown on the rigidsubstrate, the rigid substrate has slits that extend from the first mainsurface to the second main surface and expose the bonding pads of thesemiconductor pellet, and the bonding wires extend through the slits inthe rigid substrate to connect the bonding pads and the electrode pads;wherein the bonding pads are arranged at the periphery of thesemiconductor pellet and the slits are formed along the directions ofrows of the bonding pads.
 12. A semiconductor device according to claim11, wherein the electrode pads are located on both sides of the slits.13. A semiconductor device according to claim 12, wherein the electrodepads located on one side of the slits and under the semiconductor pelletare power supply pads, and the electrode pads located on the other sideof the slits and outside the semiconductor pellet are signal pads.
 14. Asemiconductor device comprising:a substrate of a quadrilateral shapehaving a first pair of opposed edges and a second pair of opposed edges,said substrate having a first main surface, a second main surfaceopposite to said first main surface and a first slit and a second sliteach extending from said first main surface to said second main surface,said first slit extending along one of said first pair of opposed edges,said second slit extending along the other of said first pair of opposededges, said substrate having first electrode pads on said second mainsurface in a first area between said first and second slits, secondelectrode pads on said second main surface in a second area between saidfirst slit and said one of the first pair of opposed edges, and thirdelectrode pads on said second main surface in a third area between saidsecond slit and the other of the first pair of opposed edges; asemiconductor pellet having a main surface with semiconductor elementsand bonding pads, said semiconductor pellet being mounted on said firstmain surface of substrate such that said bonding pads are arranged to bein line with said first and second slits; bonding wires extendingthrough said first and second slits in said substrate and electricallyconnecting said bonding pads and said first to third electrode pads,respectively; a resin member sealing said semiconductor pellet and saidbonding wires; and bump electrodes arranged on said second main surfaceof said substrate in said first to third areas in a direction of saidfirst pair of opposed edges and being electrically connected with saidfirst to third electrode pads, wherein said bump electrodes in saidsecond and third areas are arranged to form plural rows in a directionof at least one of said second pair of opposed edges, respectively. 15.A semiconductor device according to claim 14, wherein said semiconductorpellet has a quadrilateral shape and has a third pair of opposed edgesand a fourth pair of opposed edges, wherein said bonding pads arearranged in a peripheral portion of said main surface and extend alongsaid third pair of opposed edges.
 16. A semiconductor device accordingto claim 15, wherein said semiconductor pellet is mounted on said firstmain surface opposite to said first area, wherein said substrate has alarger size than that of said semiconductor pellet, and wherein saidbump electrodes in said second and third areas are located outside saidthird pair of opposed edges.
 17. A semiconductor device according toclaim 14, wherein the number of said bump electrodes in said second andthird areas is larger than the number of said bump electrodes in saidfirst area.
 18. A semiconductor device according to claim 14, whereinsaid semiconductor pellet has a rear surface opposite to said mainsurface, and wherein said rear surface of said semiconductor pellet isexposed from said resin member.
 19. A semiconductor device according toclaim 14, wherein the number of said bump electrodes in said second areais larger than the number of said bump electrodes in said first area.20. A semiconductor device according to claim 14, wherein saidsemiconductor pellet has a rear surface opposite to said main surface,and wherein said rear surface of said semiconductor pellet is exposedfrom said resin member.
 21. A semiconductor device according to claim14, wherein said first electrode pads extend along said first and secondslits, respectively, said second electrode pads extend along said firstslit, and said third electrode pads extend along said second slit,wherein said first to third electrode pads are arranged at a firstpitch, respectively, wherein said bonding pads in said first and secondslits are arranged at a second pitch which is smaller than said firstpitch, respectively, wherein said bonding wires in said first slitalternately connect said bonding pads in said first slit with said firstand second electrode pads, and wherein said bonding wires in said secondslit alternately connect said bonding pads in said second slit with saidfirst and third electrode pads.
 22. A semiconductor device comprising:asubstrate of a quadrilateral shape having first to fourth edges, saidsubstrate having a first main surface, a second main surface opposite tosaid first main surface and first to fourth slits extending from saidfirst main surface to said second main surface, said first to fourthslits respectively extending along said first to fourth edges anddefining a first area of said substrate surrounded by said first tofourth slits and a second area of said substrate extending outside saidfirst to fourth slits, said substrate having first electrode pads onsaid second main surface in said first area and second electrode pads onsaid second main surface in said second area; a semiconductor pellethaving a main surface with semiconductor elements and bonding pads, saidsemiconductor pellet being mounted on said first main surface ofsubstrate such that said bonding pads are arranged in line with saidfirst to fourth slits; bonding wires extending through said first tofourth slits in said substrate and electrically connecting said bondingpads and said first and second electrode pads, respectively; a resinmember sealing said semiconductor pellet and said bonding wires; andbump electrodes arranged on said second main surface of said substratein said first and second areas and being electrically connected withsaid first and second electrode pads, wherein said bump electrodes insaid second area are arranged to form a plurality of rows such that saidplurality of rows are formed relative to one another to surround saidfirst area of substrate.
 23. A semiconductor device according to claim22, wherein said semiconductor pellet has a quadrilateral shape and hasfirst to fourth edges, wherein said bonding pads are arranged in aperipheral portion of said main surface and extend along said first tofourth edges of said semiconductor pellet.
 24. A semiconductor deviceaccording to claim 23, wherein said semiconductor pellet is mounted onsaid first main surface opposite to said first area, wherein saidsubstrate has a larger size than that of said semiconductor pellet, andwherein said bump electrodes in said second area are located outsidesaid first to fourth edges of said semiconductor pellet.
 25. Asemiconductor device according to claim 22, wherein said first andsecond electrode pads extending along said first to fourth slits,respectively, and are arranged at a first pitch, wherein said bondingpads extend along said first and second electrode pads and are arrangedat a second pitch which is smaller than said first pitch, and whereinsaid bonding wires alternately connect said bonding pads with said firstand second electrode pads.